Multistage centrifugal blower with spiral casings



Oct. 4, 1949. KARRER 2,483,643

MULTISTAGE CENTRIFUGAL BLOWER WITH SPIRAL CASINGS Filed Nov. 20, 1945 Patented o 1949 MULTISTAGE CENTRIFUGAL BLOWER WITH SPIRAL CASINGS Josef Karrer, Zurich, Switzerland, assignor to Atelier-s de Construction Oerlikon, Oerlikon, Switzerland, a corporation of Switzerland Application November 20, 1945; Serial No. 629,878 In Switzerland July 29, 1939 Section 1, Public Law 690, August 8, 1946 i Patent expires July 29, 1959 The centrifugal blowers (fans and com pressors) with spiral casing hitherto designed operate in such a manner that the rotor .wheel conveys the medium drawn in to the spiral. In these cases the spiral casing can be designed only as a collecting chamber, that is to say, the 5 Another drawback of known designs consists medium continues to flow on with approximatein the casings being designed considerably wider ly the same velocity at the outlet of the rotor than the rotor wheel, with the result that the wheel in the spiral, and the velocity is converted media, after discharge from the rotor are deinto pressure in a difiusor outside the spiral. flected laterally, which again leads to losses. The spiral casing may also be designed with an This disadvantage also is elf .iinated with the increased cross-section for the purpose of consubdivided spiral casing. For, by subdividing verting the velocities into pressure already in the the spiral and transferring the principal convers ir l sion of velocity into pressure to the outside of Both constructions are connected with great said spiral, the cross sections of the partial disadvantages; in both cases the media entering spirals may be reduced to such a. degree that the the casing at the beginning of the spiral are dewidth of the spiral may be diminished approxifiected 360 up to their discharge from the spiral. mately to that of the rotor wheel, or that at As the media entering the casing at the end of least the widening toward the outside does not the spiral from the rotor wheel continue to flow exceed an angle of 20 and the height of the on in a straight line, the media suffer a mean respiral does not exceed double the width of the flection of 180. If the great velocities are taken rotor wheel, whereby favorable flowing condiinto consideration, especially in blowers and tions are obtained. compressors, it will be readily seen that great If, ior instance, the spiral casing has three losses must occur in the spirals as made today. 5 partial spirals I, II, III, the mean deflection is If the spiralcasing is also designed as a diffusor only 60, and the loss drops to about 70 of that the mean velocities, it is true, become smaller and of a blower of the usual design. With more consequently also the losses of flow. However, partial spirals the loss becomes still smaller; designing the spiral casing as a difiusor produces however, too great a subdivision, more than six, other drawbacks. The great velocities obtaining produces hardly any gain. at the inlet of the spiral are gradually converted 0 the p al Spirals e jo d the difillSOrS, into pressure at least partially. The velocity dein which the Pressure Conversion takes place creases toward the outlet, and the static pressure P p y e difiusers y be in e p e of increases. This takes place especially at the h Spiral h deflected according to the condiouter circumference. At the inner circumferthe deslgnence new media always enter the spiral from the theFase smgle blower and 1f the rotor wheel, and as here the velocities have not gf g l fi fif ggi gi f gg gg 3 i g o ay e o a yet bfeen cmiverted presstue the Statm pressingle outlet, for example by lengthening two sure 15 Smal er at t e mner cumtmference caus- 40 diiiusers and leading them to the third. Such ing transverse currents and vortices to appear. lengthening and deflection causes only small In to ehmmate w advantage? the losses, as the cross section may be made small in invention proposes subdividing, m a centrifugal this case, and the velocities thus kept blo With Spiral Casing, Said Spiral a ing into In the case of multiple stage designs,- the t least tWO Partial spirals, with Ors joinin partial difiusers are ledlby transfer conduits into the spirals. In that way the mean deflection the suction chamber of the following stage. can drop at least to 90, in the case of three Of course, the invention may be applied to all spirals t 0, it four t 45, t Th losses centrifugal machines with spiral casings for air of deflection can thereby be reduced to very small gasemls media values; for example, for the various angles of de- In the accompanymg drawmgsi fiectlon the following coefficients of resistance are Figs 1 2 elevatlqnal and transverse found cross-sectional views respectively of a blower of usual design. 30 180 Figs. 3, 4, and 5 are elevational, diagrammatic, 0.03 0.90 0.2 0.42 55 and bottom plan views, respectively, the last view 1 Claim. (01. 230-) By transferring the principal conversion of pressure to the outside of the spiral, different pressures are moreoveravoided as much as possible, thus obtaining the smallest losses and the highet degree of efiiciency.

being partially in cross-section, of a multi-stage centrifugal blower constituting the invention.

The annexed drawings explain the subject matter of the invention. Figs. 1 and 2 show a view and section respectively of a blower of the usual design, with a blower wheel I and a spiral casing 2. 3 is a diffuser built on to it. The filament of flow entering at A the spiral casing 2 will move on at the other circumference and up to the outlet undergoes a deflection of 360 at point B. The last filament of flow enters at B (A) the casing from the rotor wheel and does not undergo any deflection. Therefore, the mean of the deflection of the medium is 180". I

Figs. 3, 4, 5 show a multiple stage centrifugal blower. The two rotor wheels 4 and 5 (Fig. 5) are carried by the shaft 6 and convey into the spiral casings I; II; III; IV. In the diffusers I; II; III; IV the velocity is converted into pressure. By means of the transfer tubes 1'; II"; III"; IV" the air is conveyed to the suction chamber 1 of the second stage. The rotor wheel 5 draws it from the chamber 1 into which the transfer tubes 1''; II"; III"; IV" discharge. The second stage also has four partial spirals and four difiusers. The four transfer tubes discharge into the outlet chamber 8 through the connections I'; II'; III'; IV, Fig. 4. 9 is a common discharge, for the medium.

Having thus described my invention, I claim: A multi-stage centrifugal blower having the combination of a leading and a succeeding rotatable fluid impeller, the peripheral region surrounding said leading impeller having therein a plurality of exposed sectoral spiral casings constituting the housing of the blower, each of said casings receiving fluid from its impeller for therethrough evolving a high velocity of the fluid, said pluralities of casings jointly producing a total increase of efllciency with reduction of losses of the centrifugalblower, an exposed diffuser for each of said casings joined to the outlet thereof for converting the velocity of its fluid into pressure, and a branching conduit for and joined to each of said diffusers and to the inlet of the suction chamber of said succeeding impeller transferring the fluid coursing from its said leading impeller, its said casing, and its said difluser into the suction chamber of said succeeding impeller.

- JOSEF KARRER.

REFERENCES CITED.

The following references are of record in the flle of this patent:

FOREIGN PATENTS Number Country Date 170,815 Great Britain Oct. 14, 1921 218,454 Switzerland Apr. 1, 1942 542,468 Great Britain Jan. 12, 1942 600,975 France Nov. 21, 1925 i i i l l 

